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The year 2012, according to Twitter, was about politics, lost celebrities, great sports moments and people around the world tweeting all about it.

Twitter on Tuesday released a look at what it's calling the Year on Twitter, a roundup of the hottest topics on one of the world's most popular social networks. The list highlights top moments of the year, along with the top tweets, retweets and tweeters.

"Every day, we're amazed and humbled by the many ways in which people use Twitter, which range from simply retweeting to igniting conversations with hashtags to sharing spectacular and far-flung views," wrote Karen Wickre, an editorial director at Twitter, in a blog post. "In 2012, everyone on Twitter brought us closer to moments and places that used to be far away or inaccessible."

One of the most memorable tweets, came from President Barack Obama shortly after he was re-elected to a second term as president in November. Obama tweeted a picture of him hugging his wife, Michelle, with the words, "Four more years."

The tweet had nearly 817,000 retweets.

According to Wickre, Obama's was the most retweeted tweet of the year, as well as the most retweeted ever on Twitter. Retweets of that message came from people in more than 200 countries.

Some tweets were literally out of this world.

On Oct. 29, NASA's Mars Curiosity rover or someone from its Earth-based team tweeted a photo of a Martian rock and noted that it was using its hand-lens camera to take photos on the surface of Mars.

"MAHLI Rocks! Used my hand-lens imager to take pics of rocks in the Rocknest area for future examination http://twitpic.com/b8lps7," tweeted @MarsCuriosity.

On Oct. 30, astronaut Sunita Williams tweeted about the devastation from super storm Sandy while onboard the International Space Station.

From another frontier, movie director James Cameron tweeted from the depths of the Mariana Trench, considered the deepest part of the world's oceans. Writing from 35,755 feet beneath the surface of the ocean, he tweeted, "Just arrived at the ocean's deepest pt. Hitting bottom never felt so good. Can't wait to share what I'm seeing w/ you @DeepChallenge"

Among the events creating some of the biggest Twitter conversations were the Summer Olympics, which generated 150 million tweets, and the U.S. presidential election. The first presidential debate produced 10 million tweets alone.

Hurricane Sandy, which reached U.S. shores on Oct. 27, generated more than 20 million tweets, including tweets seeking help, donations and information on where to seek shelter.